This invention relates to the casting of metal strip. It has particular application to the casting of metal strip by continuous casting in a twin roll caster.
In a twin roll caster molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The term xe2x80x9cnipxe2x80x9d is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or series of vessels from which it flows through a metal delivery nozzle located above the nip so as to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in sliding engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electromagnetic barriers have also been proposed.
The change-over of the casting rolls in a twin roll caster is a significant problem. The rolls may need to be changed between casts so as to allow a different width of strip to be cast and the rolls must be replaced if the casting surfaces are in any way damaged or deteriorate during casting. If the rolls have to be changed in situ, a significant amount of potential casting time is lost waiting for the casting components and the area surrounding them to cool. The new set of rolls, once in place, has to be calibrated prior to casting so that the nip width can be pre-set.
When casting ferrous metals, it is necessary to preheat the refractory components of the metal delivery and pool confinement means to very high temperatures before casting commences. For these reasons it has been proposed to build twin roll casters with demountable components so that the rolls and preheated refractory components can be rapidly brought together into an operative assembly and casting started before the preheated components cool significantly. One example of a caster with moveable rolls and refractory components is disclosed in our Australian Pat. No. 631728 and 637548 and corresponding U.S. Pat. No. 5,184,668 and 5,277,243.
The present invention enables a twin roll strip caster to be built with a modular construction in which the casting rolls are installed in a moveable module readily moveable into and out of the machine. A previous proposal for mounting the rolls on a moveable module is described in Japanese Patent Publication JP-B93-9185 of Mitsubishi Heavy Industries Ltd. In that proposal the rolls and the pool confining side plates are mounted together on a frame which is carried on a wheeled car moveable horizontally into and out of the machine along rails. The present invention provides a different arrangement in which a roll module is moved horizontally into an intermediate position beneath the final casting position and is ;then lifted into the casting position. This enables the rolls to be quickly manoeuvred into the casting position without requiring movement of any ancillary equipment or components. In a preferred embodiment of the invention the rolls can be lifted into position between a pair of pool confinement side plates without the need to move the side plates.
According to the present invention there is provided an apparatus for continuously casting metal strip which includes: a pair of parallel casting rolls forming a nip between them; metal delivery means to deliver molten metal into the nip between the rolls to form a casting pool of molten metal supported on casting roll surfaces immediately above the nip; pool confining means at the ends of the rolls confining the pool against outflow from the ends of the nip; and roll drive mean""s to drive the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip; wherein the casting rolls are mounted on a roll module installed in and removable from the caster as a unit and movable horizontally transversely to a casting direction from a stand-by position to an intermediate position beneath a casting position of the rolls and thereafter vertically to lift the rolls to the,casting position; and wherein the apparatus includes a lifting means for lifting the roll module and rolls mounted thereon from the intermediate position to the casting position.
Preferably the lifting means includes a fluid cylinder actuated hoist.
Preferably the apparatus includes drive coupling means which automatically couple the roll drive means to the casting rolls when the roll module is in the intermediate position.
Preferably the apparatus includes water coupling means which automatically couple a water cooling means to the rolls when the roll module is in the intermediate position.
Preferably the roll module further includes a module frame and roll carriers moveable on the module frame to permit bodily movement of the rolls toward and away from one another to vary the nip between them.
Preferably the apparatus further includes a roll biasing means operable when the roll module is in the casting position to move the casting; rolls from an open position towards each other to vary the width of the nip.
Preferably the pool confining means is in the casting position prior to moving the roll module from stand-by position to the intermediate position and thereafter to the casting position. Moving the roll module to the intermediate position beneath the casting position and holding the casting rolls in the open position ensures that there is no contact between the rolls and the pool confining means during the installation of the rolls.
Preferably the roll biasing means is operable to move the casting rolls away from each other.
Preferably the roll module further includes an adjustable stop means disposed beneath the nip and between the roll carriers to serve as a spacer stop for engagement with the roll carriers to pre-set the minimum width of the nip between the rolls and adjustable in width to vary the minimum width of the nip.
Preferably the roll biasing means is operable to move the casting rolls from an open position to the stop means and thereafter to bias the rolls against the stop means.
Preferably, the roll module further includes a means for holding the roll carriers, in the open position.
Preferably the holding means includes a locking pin assembly having locking pins carried by the module frame that can be received in openings in the roll carriers.
Preferably the locking pins are fixed relative to the roll carriers so that when the roll carriers and the rolls thereon are lifted from the intermediate position to the casting position the roll carriers are moved clear of and therefore are not retained by the locking pins.
The roll carriers may comprise a pair of roll end support structures for each of the rolls disposed generally beneath the ends of the respective roll.
Each pair of roll end support structures may carry journal bearings mounting the respective roll ends for rotation about a central roll axis.
The roll end support structures may be mounted on the module frame for generally horizontal movement of the rolls toward and away from one another.
The module frame may be moveable horizontally on linear bearings into and out of the intermediate position in the caster.
The roll module may be firmly clamped vertically by operation of the fluid cylinder actuated hoist described above lifting the roll module so that stop surfaces on the roll module contact fixed stop surfaces on the caster.
Appropriate indexing means May be provided for indexing of the module frame with the main machine frame when the module frame is hoisted so as to provide for accurate positioning of the module frame longitudinally of the rolls.
The roll biasing means may include a pair of biasing units for each roll and the biasing units being connectable to the roll carriers.
The biasing units may be carried on moveable mountings on the caster so that they can be readily moved into and out of operative inter-engagement with the roll carriers.
The invention also provides apparatus for continuously casting metal strip comprising a pair of parallel casting rolls forming a nip between them; metal delivery means to deliver molten metal into the nip between the rolls to form a casting pool of molten metal supported on casting roll surfaces immediately above the nip; pool confining means at the ends of the rolls against outflow from the ends of the nip; and roll drive means to drive the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip; wherein the casting rolls are mounted on a roll module installed in and removable from the caster as a unit, said module comprising a module frame; roll carriers moveable on the module frame to permit bodily movement of the rolls toward and away from one another to vary the nip between them; and adjustable stop means disposed beneath the nip and between the roll carriers to serve as a spacer stop for engagement with the roll carriers to pre-set the minimum width of the nip between the rolls and adjustable in width to vary the minimum width of the nip.
According to the present invention there is also provided a method of positioning casting rolls in a continuous strip caster which includes the steps of: moving a roll module carrying a pair of parallel casting rolls horizontally in a direction transverse to a casting direction from a stand-by position to an intermediate position; coupling the rolls to a roll drive means and a water cooling unit at the intermediate position; and lifting the roll module to a casting position.
Preferably, the roll drive means and the water cooling unit are automatically coupled to the rolls when the roll module is moved to the intermediate position.
Preferably, after lifting the roll module to the casting position, the method further includes moving the rolls inwardly to a pre-set nip position.
Preferably, the rolls are held apart prior to being lifted to the casting position and the lifting movement releases the rolls for inward movement.